The increasingly available, highly integrated circuit arrangements in the form of modules structured of individual semiconductor chips comprise in accordance with the higher degree of integration the equally increasing difficulty of detecting error-containing semiconductor circuits. This applies in particular if the functional units represented by semiconductor circuits comprise combinational circuits and sequential circuits.
One way of detecting minimum replaceable units containing faulty storage elements is for each minimum replaceable unit to have its own specific associated test conductor terminal. Then in an individual test the respective test conductor terminal could be referred to for error display. Such steps are, however, prohibitive since they would not only require an inadmissibly high number of additional terminals requiring a corresponding amount of space which is not easily available for elements of a high degree of integration, but which due to the necessary individual testing would require a considerable amount of time. Furthermore, in a testing of highly integrated semiconductor circuits containing sequential circuits a functional test is very difficult since for that purpose and for a clear error detection the respective storage states have to be known in advance. In other words, prior to the execution of a functional check the storage elements have to be brought into known states, or the states have to be determined.
According to a testing device described in German Offenlegungsschrift No. 23 49 324 [corresponding to U.S. Pat. No. 3,761,695 fully identified supra] this can be achieved by setting a test pattern in the monolithically integrated semiconductor circuits. Of course under the condition that the functional unit to be tested is converted for testing, from a circuit system into a network, i.e. from a sequential circuit into a combinational circuit. Each storage element is a shift register stage containing a master flipflop and a slave flipflop. The flipflops being d.c. latches. All storage elements of a functional unit to be tested can be combined into one single shift register divided into individual segments. The shift register segments being considered minimum replaceable units.
The disclosures of U.S. Pat. Nos. 3,783,254, 3,761,695 and 3,784,907 (each fully identified supra) are incorporated herein by reference thereto to the same extent as though the specification and drawings of said patents were expressly set-forth herein. The first test is for the shift register function in order to find out whether the shift register operates correctly. If no error is found there follows the test for level sensitivity (level sensitive control). For that purpose, all shift register levels are set into a specific known state in order to eliminate all influences of the storage history. For a thorough examination, however, several hundreds of test patterns, i.e., state combinations of the shift register stages have to be used so that, as pointed out above, a considerable number of process steps is required. A correspondingly complex and complicated process has to be applied for detecting a specific segment, i.e., a minimum replaceable unit containing the cause of an error. However, the precise detection of and consequently the possibility to exchange a faulty segment will have to be achieved, since this will considerably facilitate operation and maintenance of a complex system. In order to arrive at that aim in the least complicated manner additional circuit component terminals and line metallizations are required which in a highly integrated monolithic semiconductor circuit would require considerable supplementary means. These include in particular, pins and the space they require on a module or chip, if it is considered additionally that the main effort in highly integrated semiconductor circuit technology is to keep the ratio between number of pins and number of circuits as low as possible. As pointed out above, however, this is not possible if there is to be an error detection down to a minimum replaceable unit by means of the known steps.